Availability of cadmium (Cd) and nitrate and their transfer to green leafy vegetables is highly dependenton physical, chemical and biochemical conditions of the soil. The phenotypic characteristics, accumulationof hazardous materials and rhizosphere properties of two ecotypes of water spinach in response towater stress were investigated. Flooding significantly enhanced plant growth and decreased Cd andnitrate concentrations in the shoot and root of both ecotypes of water spinach. Flooding extensivelychanged the physicochemical properties and biological processes in the rhizosphere, including increasedpH and activities of urease and acid phosphatase, and decreased availability of Cd and nitrate and activityof nitrate reductase. Furthermore, flooding increased rhizosphere bacteria community diversity(including richness and evenness) and changed their community structure. Denitrifying bacteria (Clostridiales,Azoarcus and Pseudomonas), toxic metal resistant microorganisms (Rhodosporillaceae, Rhizobialesand Geobacter) were enriched in the rhizosphere under flooding conditions, and the plant growthpromotingtaxa (Sphingomonadaceae) were preferentially colonized in the high accumulator (HA)rhizosphere region. These results indicated that flooding treatments result in biochemical and microbiologicalchanges in soil, especially in the rhizosphere and reduced the availability of Cd and nitrate toplants, thus decreasing their uptake by water spinach. It is, therefore, possible to promote crop growthand reduce the accumulation of hazardous materials in vegetable crops like water spinach by controllingsoil moisture conditions.
Fig. 7. Least discriminant analysis (LDA) of affected size taxonomic cladogram for comparing rhizospheric soil samples collected from the two water spinach genotypes underdifferent water management. The discriminant taxon nodes are colored, and branches are shaded according to the highest ranked group for that taxon. If the taxon did not representsignificant differences among sample groups, the corresponding node is colored yellow. Selected highly abundant taxa are denoted with letters. (For interpretation of the referencesto color in this figure legend, the reader is referred to the Web version of this article.)